As this project appears to be fairly unknown in the fediverse still, I’d like to use this opportunity to advertise Flohmarkt. This Fediverse equivalent of Facebook Marketplace already has some instances up and running - see here: https://codeberg.org/flohmarkt/flohmarkt/wiki/flohmarkt-instances
So you only trade with people in your web of trust? That’s not feasible. People flock to these websites to trade with strangers. You don’t need a middleman to trade with people you already trust.
Friend of friend networks, that’s how classmates have benefits created ( a prototype to “prove” 6 connections theory )